Two circles with centres A and B touch each externally, PQ is a direct common tangent which touches the circle at P and Q. If the radii of the circles are 9 cm and 4 cm, respectively, then the length of PQ (in cm) is equal to:
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 12.
Length of direct common tangent = √[d2 - (R - r)2]
d = 9 + 4 = 13 cm
PQ = √[132 - (9 - 4)2] = √[169 - 25] = √144 = 12 cm
Hence, the value of PQ is 12 cm.